Production And Selective Electron Beam Melting Of NiTi Powders By PREP

NiTi alloy possesses a series of excellent properties,such as unique shape memory effect,superelasticity,low elastic modulus,high damping,good biocompatibility,excellent corrosion resistance,and so on.It's obtained extensive applications in the field of aerospace,biomedicine,automobile manufacturing,and the like.However,it can only be processed into simple shapes because of its high chemical reactivity,poor thermal conductivity,excellent ductility and other disadvantages.These problems restrict further application and development of NiTi alloy severely.The newly additive manufacturing technology,one of the rapid clean manufacturing methods,offers a possibility to achieve process of complex shape structure NiTi alloy.Compared with other additive manufacture,selective electron beam melting has unique advantages,such as high energy utilization efficiency,no pollution in vacuum,low residual stress,especially suit for the high chemical reactivity alloys.It is expected that NiTi alloy SEBM technology will have a broad prospects.Based on the above,this study make attempt to explore the process of NiTi alloy fabricated by SEBM.Main research contents include the preparation of NiTi alloy powders by plasma rotating electrode process and manufacture of the deposited NiTi alloy by SEBM.The microstructure and properties of NiTi alloy powder and rods samples were characterized by OM,SEM,DSC and XRD.Tensile testing machine was utilized to explore the application feasibility of this SEBM process to prepare NiTi alloy powder and deposited NiTi alloy.Several conclusions are obtained:1.The size distribution of PREPed NiTi alloy particle powders is mainly from 44 to 150?m.The particle diameter of yielded NiTi alloy powder below-150 ?m is more than 88%.More than 90%of the spherical particles exhibits a good fluidity of 19.7 s/50 g.The apparent density is 4.03 g/cm3.All the characteristics satisfy the requirement of NiTi alloy powders,which is used for the electron beam selective melting technology.2.The diameter and height of NiTi alloy rods is 12 mm and 70 mm respectively,which were fabricated by SEBM technology.The density of NiTi alloy samples is 6.48 g/cm3,reaching to 99.6%of the theoretical density.The microstructure of NiTi alloy presents a strong columnar grain and the crystals are refined along deposition direction.3.The NiTi alloy fabricated by SEBM experienced a two-step of B2?R?B19'phase transformation during cooling,while it exhibits a two-step martensitic transformation during cooling.The phase transition temperature have no clear change with different height of deposited layer and is lower than 15?.Average ultimate tensile strength of NiTi alloy is 1411.0 MPa,which is higer than the NiTi strength standard of ASTM F 2063-05.